A "composite" is a material composed of thermoplastic resin and reinforcing fibers, e.g. graphite or glass fibers.
It is known to manufacture articles from a composite by molding the composite on a forming tool. For example, a resin impregnated graphite or glass cloth is applied in layers onto a forming tool. Then, a vacuum bag is applied over the composite and the forming tool and the bag is evacuated so that atmospheric pressure will push the bag into pressure exerting contact with the composite.
The vacuum bag material is flat and when the vacuum is applied it becomes wrinkled as it tends to take the shape of the forming tool. If the bagging material were allowed to directly contact the composite material, or to be separated from the composite material by only a release film and breather material, there would be a resin build-up in the voids of the wrinkles. This would necessitate substantial machining of the cured composite article in order to provide it with a suitable finished surface.
It is known to substantially prevent wrinkling by positioning a pressure pad against the uncurved composite article, between it and the vacuum bag. The pressure pad is constructed to have an inner surface which substantially conforms in size and shape to the composite part being manufactured.
The pressure pads are themselves molded on a form. A suitable uncured, heat curable elastomer is applied to the form, so as to cover the form to a desired pad thickness. Then, a vacuum bag is applied to hold the uncured elastomer tight against the forming tool. Then the forming tool/elastomer assembly is placed into a chamber and the chamber is subjected to heat and pressure for curing the elastomeric member.
A problem with heat curing elastomers is that the curing process causes them to shrink. Although minimum shrinkage elastomers have been developed, none have totally eliminated the shrinkage problem. Because of the shrinkage, it has been the practice to construct a forming tool for the pads that is oversized to such an extent that an elastomeric pad made on it will, following shrinkage, be approximately the right size. A problem of manufacturing pressure pads in this matter is that the forming tool used for making the pressure pad is expensive. Such a forming tool must be made for each part and the forming tools must be stored somewhere between periods of use.
The present invention provides a way of manufacturing pressure pads without the need to manufacture special forming tools.